Trying to wrap my mind around this...

Ok, I've told my story before, but my mind still can't get past some of it understand the next step. I'll repost and update it here and maybe some kind soul out there can help me "get this".

Last April(2003), I bought this 300 SD. Has 300,000 plus. Runs very strong. THe guy I bought it from said it leaked about 1 qt every 500 miles. It had had a top end job a few years earlier. I took it for a pre purchase inspection at a reputable shop with a certified mercedes mech. They detailed some things that needed to be fixed, some possible places the oil leak was coming from, and basically told me this was a strong car, had no blowby, and I should get it. Got the engine cleaned because it was so covered, and then took it in for inspection. They did a valve job, checked for leaks, decided it was burning oil, not leaking that much. They suggested the turbo, or the rings (they checked the vaccuum, it's not that). I got pissed at them at this point, and went to someone else.

My turbo blew on the road and I had it replaced, this did not solve the problem. The new mech ( a good guy) told me I had tons of blowby and should just drive the car into the ground and keep it above the min line for the oil in the meanwhile. He replaced the valve stem guides also, as a last ditch when the new turbo didn't stop the oil consumption.

I've been trying Auto RX in it, it's not really helping that much except with the small leak on the oil filler cap. I'm on my first cleanse after my first Auto RX treatment, for 2000 miles(500 more to go), then another Auto rx round. There are some oil leaks that I maybe should try to fix, but they seem small. I've placed a drip pan under the car and only get a few drips a day. This car is in nice shap on the inside, not pristine, but good, solid, uncracked dash, ac works etc. Only tach and cruise doesn't work. Have had some electrical window gremlins lately, but I think that is the relay now (thanks to this forum).

I tried running a diesel rated oil in in,but they are too thin (unless there is a 20-50 rated C oil) so I have to stick with the 20-50 oil. I go through it so fast that I buy it by the case.

My problem is this, how can a car be so fundamentally broken yet run so strong and good? I just don't get it. A car at the end of it's life should sound and act like it. This one doesn't.

I am considering writing the "reputable shop" (the one that did the lousy prepurchase, they have a really big good reputation here) but I don't know what I would want out of them.

I am also considering contacting the seller, even though I purchased as is, because he mis represented or was mistaken about the oil usage.

And what do I do about my car? I don't have a lot of $ and losing this $2000 purchase price and $1000 in trying to get it together on bad advice is really challenging to me.

I appreciate all ideas and help. Thanks.